FIG. 1 shows a typical shaped charge 10 having a metal jacket 11 or a charge case 11. High explosive material 13 is disposed inside the metal jacket 11. A liner 12 retains the explosive material in the jacket 11 during the period prior to detonation. A primer column 15 provides a detonating link between a detonating cord 16 and the explosive 13.
When the shaped charge 10 is detonated a portion of the liner 12 forms a jet portion of the liner. The jet is propelled away from the jacket 11 in a direction 17 toward a target. Another portion of the liner 12 is propelled away from the jacket 11 and forms what is known as a slug or carrot portion of the liner. The slug or carrot portion is not propelled to the same extent as the “jet”. When the shaped charge 10 is used in a perforating gun, the target is normally a cased downhole formation. Upon detonation, the jet portion of the liner 12 is propelled through the casing and penetrates the downhole formation to enhance recovery of downhole hydrocarbons. The slug portion, on the other hand, is designed to break up upon contact with the casing.
Only about 25-30 percent of the shaped charge liner mass is converted into the jet. The jet density, velocity profile, jet material, jet straightness, and target properties determine the ability of the jet to penetrate a given target. While the slug portion does not contribute much to the penetration of the shaped charge, the slug should have certain properties that contribute to system performance. For example, the slug should break up and not plug the perforation tunnel in the target.
Liners for shaped charges have been fabricated using pure metals, alloys and/or ceramics. The metals used to form the liners can be powder materials, which may, for example, comprise tungsten, lead or copper. When the latter liners have been used, about 75 percent of the tungsten, i.e. that portion of the tungsten in the slug portion, is not converted into the jet. Since tungsten comprises the bulk of such powder and since tungsten is quite expensive, a substantial amount of money is wasted by fabricating the slug portion of a shaped charge with tungsten.
Liners for shaped charges have been fabricated using different solid materials for the jet and the slug. One such example of a liner utilizing solid copper for the jet and solid zinc for the slug.